Just five days after the Australian Capital Territory’s new equal marriage law comes into effect, it could be deemed unconstitutional in a High Court ruling.

The equal marriage bill which passed in the ACT in October is due to come into effect on 7 December, and the High Court has reserved the 12th to make a ruling in a challenge by the federal government which states that the law goes against the federal Marriage Act.

The highest legal jurisdiction in Australia, a full bench of the court, heard a challenge from the Commonwealth on Tuesday, which sought to have the same-sex marriage bill struck down, and will announce its ruling on 12 December.

The Commonwealth asked the court to consider eight questions in arguing that the new law violates the federal Marriage Act, which it sees as a sole code to abide by, and the ACT defended its law saying it did not do so.

According to Bloomberg, 47 couples are scheduled to marry in the five-day window, and will be allowed to do so unless the Commonwealth seeks an injunction to halt the issue of marriage certificates.

Despite having a gay siblingAustralia’s Prime Minister Tony Abbott continues to oppose equal marriage and has supported efforts to halt the ACT’s equal marriage bill in the courts.

In October,, Mr Abbott said that the ACT court challenge was about upholding the Australian constitution and about preserving a “uniform approach throughout the commonwealth” to marriage laws.

Earlier, several amendments were made to the ACT’s bill in order to safeguard its legal passage. 

Same-sex couples living in the ACT have been allowed to register their partnerships since 2008 and hold civil partnership ceremonies since 2009, when the ACT became the first territory in Australia to introduce such legislation.

Equal marriage remains banned at a federal level in Australia and efforts to legalise the measure failed in the Australian Parliament in September 2012.

Christine Forster, the sister of Mr Abbott, has revealed that she has proposed to her partner Virginia Edwards.